Many well-known warp-knitted fabrics are made on knitting machines that have three or more guide bars, at least two of which incorporate threads into the fabric as lay-ins in the chain network. A third guide bar, and perhaps additional guide bars, deliver a third set, or additional sets, of threads to the needles to form the chain stitching.
In warp-knitted fabrics in which two or more guide bars deliver lay-ins exclusively and one or more guide bars deliver threads that are knitted into warp-wise chains, there are many known examples in which one of the sets of laid-in threads from one guide bar is dominant and the other set is recessive. For example, a known open-mesh fabric made on Rachel machines involves forming warp-wise chains from threads delivered by the front guide bar set up on the formula, 02/20, and two sets of lay-ins are delivered by two additional guide bars, as follows:
Guide Bar II, 00/22/00/66/44/66; PA1 Guide Bar III, 44/22/44/00/22/00.
Of the two sets of lay-ins in that fabric, the set delivered by guide bar II is dominant or aggressive, and the set delivered by guide bar III is recessive, inasmuch as between the third and fourth courses, the threads delivered by guide bar II, which moves 00/66, extend across three wales in one direction while the threads from guide bar III, which moves 44/00, extend across two wales in the opposite direction and then between the sixth and first courses, the threads from guide bar II (66/00) lay in from the third to the first wale while the threads from guide bar III (00/44) lay in from the second to the third wale.
It is apparent that the yarn consumption in fabrics of the types described above, as between the dominant and recessive elements of the fabric, is unequal, the dominant or aggressive elements requiring substantially more thread than the recessive elements. As far as the knitter is concerned, this means either special machine set-ups with different size yarn packages established to run out at about the same time, a solution that is of little practical value, or more downtime on the machine for rethreading and the production of relatively shorter lengths of fabric per run between rethreadings. Machine downtime is, of course, a cost factor in the total knitting operation, and minimizing downtime for rethreading increases efficiency and reduces unit costs.
The existence of aggressive and recessive elements in warp-knitted fabrics also affects the overall strength of the fabric by causing uneven stresses in the threads, depending upon whether such threads are aggressive or recessive; the recessive elements of the fabrics tend to be stressed higher than the aggressive elements under a given load, and it is therefore the recessive elements that break first and govern the overall strength.
The disadvantages of unbalanced fabric construction in warp-knitting from the point of view of increased downtime in the machine for rethreading and the desirability of balancing yarn consumption among the guide bars has been recognized in the past. See, for example, Kurz U.S. Pat. No. 3,447,345 granted June 3, 1969. The affect of the presence of aggressive and recessive elements in knit fabrics on the fabric strength has perhaps been recognized by others, but there has heretofore been no known practical way of increasing the strength without at the same time decreasing the stability of fabrics of the type here involved.